The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Multi-layered transparent composites having glass laminates with polymer interlayers and backing sheets are commonly used in a wide range of applications, where visibility, transparency, impact resistance, and safety are essential. These applications include, e.g., windshields on defense vehicles and armored vehicles, windshields on aircraft, and security enclosures in buildings, personal protection equipment, etc. Although multi-layered transparent composites and fiber reinforced plastics (FRPs) are conventionally considered to fall into the same class of materials, which is “composites,” structurally they are significantly different. Owing to the differences of these structures, their defects are also different. While considerable literature on the development, manufacturing and optimization of these multi-layer transparent composites exists, information on nondestructive evaluation (NDE) and damage detection in these composites is very limited. The result is that determining defects and damage in multi-layer structures is very difficult. For example, identifying defects that result from manufacturing issues can be nearly impossible to detect, e.g., identifying which layer resulted in the defect. This can be particularly problematic as many defects are not discernible until after the entire multi-layered transparent composite assembly has been completed, sometimes after the composite has already been deployed into use. Moreover, during use, these multi-layered transparent composites are subjected to extreme environmental conditions in addition to their normal mechanical loads, which can lead to delamination and other losses that compromise structural integrity as well as transparency of the composite.
Hence, there is a considerable need for an efficient NDE technique that can provide detailed characterization of defects/damage and in all 3-dimensions of a thick layered structure. Current Conventional techniques can only provide, at best, an estimate of the 2D (XY, in-plane) location of the defect, and optical coherence tomography (OCT) is not quite suitable for evaluation of thick multi-layered transparent composites due to important issues of beam coincidence. And none of the conventional techniques are able to provide depth (Z-axis, through thickness) information about the damage in relatively thick multi-layered transparent composites.